1. Field of the Invention
The present invention relates to a tilt-adjusting structure for an axial slide type optical pickup actuator, and more particularly to a tilt-adjusting structure for an axial slide type optical pickup actuator having a sliding surface on the protecting cover of a lens holder.
2. Description of the Prior Art
In recent years, data retrieving/recording systems for an optical disc such as a laser disc or a compact disc have been developed. In order to retrieve and record information from/to the optical disc, an optical pickup apparatus is provided for irradiating a laser beam along a track on the optical disc and retrieving data based on a beam reflected from the track. In case a track is formed in a spiral shape on the optical disc, sectors of a track have different distances from the center of the optical disc due to the eccentricity of the spiral shape. Accordingly, the tracking control operation is essential for exactly irradiating the laser beam on the track in a retrieving mode. Further, the distance between the optical pickup apparatus and the optical disc minutely changes since the optical disc is rotated in the retrieving mode. Therefore, the focusing control operation is essential since such distance change causes the exact retrieval of data to be difficult.
For the focusing control operation, a focusing error is detected from the laser beam reflected from the optical disc. A focusing error signal, which is generated when the focusing error is detected, drives the objective lens for performing the focusing control operation. In general, the objective lens is fixedly supported by a spring on an optical head housing. The optical pickup actuator having coils for moving the objective lens up and down along the axial direction of the laser beam is activated.
The optical pickup actuator as mentioned above requires a tilt adjustment during its assembling process.
Hereinafter, the tilt-adjusting structure of a conventional axial slide type optical pickup actuator will be described with reference to FIG. 1.
As shown in FIG. 1, the conventional optical pickup actuator is constituted with a cylindrical lens holder 10 and a yoke 20. The tilt-adjusting structure of the conventional optical pickup actuator comprises an optical pickup actuator, a cover 30, a tilt-adjusting plate 40, a base 50.
The lens holder 10 has an axial opening 11, penetrated from top to bottom, in the center of a cylindrical body. The lens holder 10 has a first laser beam through hole 12 and a second laser beam through hole 13 in the same radius from the axial opening 11. A first objective lens 14 is mounted in the upper portion of the first laser beam through hole 12 and a second objective lens 15 is mounted in the upper portion of the second laser beam through hole 13. Winding coils 16 are fixed 90.degree. apart to each other on the outer periphery of the lens holder 10. Magnetizable materials 17 are fixed in the center portions of the winding coils, respectively, and between the winding coils and the outer periphery of the lens holder 10. The yoke 20 is formed in a cylindrical shape to accommodate the lens holder 10. The lens holder 10 is connected with the yoke 20 by inserting a shaft 21 into the axial opening 11. The shaft 21 protrudes upwards from the center of the yoke 20. An opening 22 is formed corresponding to the first and second laser beam through holes 12 and 13. A first magnet pair 23 and a second magnet pair 24 are fixed along the inner periphery of the yoke 20, so that the first and second magnet pairs 23 and 24 correspond to the winding coils 16, respectively. A latch 25 is formed on one portion of the outer periphery of the yoke 20. Release preventing protrusions 26 are formed apart in a certain interval to each other in the radial direction on the outer periphery of the yoke 20.
The cover 30 prevents foreign materials such as dust from having contact with the lens holder 10. Further, the cover 30 has a upper plate 31 and a skirt portion 32 formed downwardly from the bottom of the upper plate 31. The upper plate 31 and the skirt portion 32 prevent the lens holder 10 from releasing in the laser beam axial direction. One portion of the upper plate 31 has a rotation limit opening 33 for limiting a rotation angle of the lens holder 10. A groove 34 is formed on the skirt portion 32 corresponding to the first latch portion 25. A release preventing opening 35 is formed corresponding to the release preventing protrusions 26. Accordingly, the cover 30 is connected with the yoke 20, the first latch portion 25 is accommodated in the groove 34, and the release preventing protrusions 26 are engaged with the release preventing opening 35.
The tilt-adjusting plate 40 is fixed on one side of the outer bottom of the yoke 20. The tilt-adjusting plate 40 has a convex tilt-adjusting surface 41. The convex tilt-adjusting surface 41 is convex toward the base 50. The base 50 has a concave tilt-adjusting surface 51 to fit with the convex tilt-adjusting surface 41. The base 50 has first and second through holes 53 and 54 at positions of forming an isosceles triangle, a vertex of which is a second latch portion 52. A first adjustment screw 55 adjusts the tilt of the optical pickup actuator. The first adjustment screw 55 is screwed through the first through hole 53 into the adjustment hole of the first adjustment portion 27 which protrudes in the radial direction from the outer periphery of the yoke 20. A second adjustment screw 56 adjusts the tilt of the optical pickup actuator. The second adjustment screw 56 is screwed through a second through hole 54 into second adjustment hole of the second adjustment portion 36 which protrudes in the radial direction from the outer periphery of the skirt portion 32. A spring 60 connects the first latch portion 25 of the yoke 20 with the second latch portion 52 of the base 50.
Operations of the tilt-adjusting structure of the conventional optical pickup actuator will be described in detail hereinafter.
The tilt adjusting plate 40 is fixed on the outer bottom of the yoke 20, and the spring 60 and the first and second adjustment screws 55 and 56 enables the yoke 20 to be mounted on the base 50. The lens holder 10 is fixedly connected with the yoke 20 through the shaft 21, and the level degree of the first and second objective lens 14 and 15 is checked. At this time, the tilt of the shaft 21 is changed by rotating the first and second adjustment screws 55 and 56 and adjusting the spring 60. When the objective lenses 14 and 15 are in a level state, the yoke 20 is fixed on the base 50.
In the meantime, in the tilt-adjusting structure of the conventional axial slide type optical pickup actuator as mentioned above, the tilt-adjusting plate 40 has a convex tilt-adjusting surface 41 for adjusting a level degree of the objective lenses 14 and 15. Further, the concave tilt-adjusting surface 51 is formed on the base 50 at a position corresponding to the concave tilt-adjusting surface 41. The second adjustment portion 36 is formed on the cover 30, and the first adjustment portion 27 is formed on the yoke 20. In particular, the convex and concave tilt-adjusting surfaces 41 and 51 are precisely machined. Unless the convex and concave tilt-adjusting surfaces 41 and 51 are precisely machined, the tilt of the optical pickup actuator may not be precisely adjusted since the tilt-adjusting plate 40 is not supported on the base 50.
Secondly, the tilt-adjusting margin is small since the yoke 20 is fixed on the base 50 and the shaft 21 protrudes upwardly from the bottom of the yoke 20.
Thirdly, more parts are required since the tilt-adjusting plate 40 is separately provided and fixed on the base 20. Accordingly, the number of manufacturing processes increases and the productivity of a product becomes low.